Recovery of benzene



March 11, 1958 .1. M. POWERS ET AL 2,826,619

RECOVERY OF BENZENE Filed June 24, 1955 umv- AROMA r/cs STREAM sa *32 35 [9 l 04 "wars /6 EX nun/01v 204v:

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John H. Powers, Y Harry E. Ciel, I

United States Patent RECOVERY OFBENZENE John M. Powers and Harry E. Cier, Baytown, Tex., as-

signors, by mesne assignments, to Esso Research and Engineering Company, Elizabeth, N. J., a corporation of Delaware Application June 24, 1955, Serial No. 517,854

9 Claims. (Cl. 260--674) The present invention is directed to a method for recovering benzene. More particularly, the invention is concerned with recovering substantially pure benzene from its mixtures with hydrocarbons. In its more specific aspects, the invention is directed to recovering substantially pure benzene from its mixtures with parafiinic and naphthenic. hydrocarbons.

The present invention may be briefly described as a method of recovering benzene in which a mixture of benzene and paratlinic and naphthenic hydrocarbons having six and seven carbon atoms in the molecule and boiling in the range between about 145 and about 170 F; is extracted with liquefied sulfur dioxide in an extraction zone under conditions to form an extract phase and a raffinate phase. The extract phase is thereafter distilled to recover an overhead fraction containing substantially the paraffinic and naphthenic hydrocarbons and a minor amount of benzene and a bottoms fraction is recovered which is substantially pure benzene.

The amount of benzene in the overhead fraction is approximately 10% by volume of the overhead fraction and is in the form of azeotropes of benzene with the non-aromatic hydrocarbons present in the extract phase.

The distillation conditions employed in distilling the extract phase will include suitable temperatures and pressures for distilling the extract phase and particularly will include a reflux ratio in the range from about :1 to about 15:1; reflux ratios ranging from about 7:1 to about 12:1 are preferred.

The overhead fraction may suitably be recycled to the extraction zone for recovery of the benzene therein.

Suitably the extract phase may have sulfur dioxide removed from it prior to charging the extract to the distillation zone for distillation.

It is contemplated that the fraction charged to the solvent extraction zone may be obtained by fractionally distilling a benzene-containing hydrocarbon such as a depentanized naphtha or a hydrocarbon mixture, for example one obtained from crude petroleum having a final boiling point of about 170 F. It is contemplated, however, that benzene-containing hydrocarbons from other sources which contain naphthenic and parafiinic hydrocarbons may also form the feed in the process.

A typical extract which may be obtained by solvent extracting a benzene-containing fraction boiling in the range between about 145 to about 170 F. is shown in Table I:

Table I Percent by volume Methylcyclopentane 10.22 Cyclohexane 0.80 Z-methylpehtane 12.78 Normal hexane 20.07 2,2-dimethyl pentane 1.81 3-methyl pentane 6.25

Benzene 48.07

The invention will be further illustrated by reference "ice to the drawing which is in the form of a flow sheet of a preferred mode. Referring now to thedrawing, numeral 11 designates a feed line by way of which. a benzenecontaining hydrocarbon is introduced into a distillation zone 12. The distillation zone 12 may be a plurality of fractional. distillation towers but for simplicitys sake is shown as a single distillation tower. It is to be understood that distillation zone 12 will include all auxiliary equipment embodied in the modern distillation tower and will be provided with suitable vapor-liquid contacting means, such as hell cap. trays. and the like, for insuring intimate contact between the liquid and the vapors. Distillation zone 12 is also provided with means for inducing reflux. Conditions of temperature and pressure are adjusted in zone 12 by heating means illustrated by a steam coil 16 to obtain an overhead fraction by way of line 17 which may boil below about 170 F. and in the range between about and about F.; a bottoms fraction may be discarded by line 15 for further processing as may be desired.

The overhead fraction from zone 12 is then introduced by line 17 into a solventextraction zone 18 which is shown diagrammatically but is. also understood to include all the necessary and auxiliary facilities of a modern extraction plant. Liquefied sulfur dioxide is introduced into zone 18 by way of line 19 and contacts the benzenecontaining fraction countercurrently to form under the conditions employed in zone 18 a raffinate phase and an extract phase. The conditions employed in zone 18 may suitably encompass a temperature in the range between about 20 F. and about -50 F. with a sulfur dioxide to benzene containing feed volume ratio in the range from about 3:1 to about 1:1. Under these conditions, the raflinate phase which is formed is withdrawn from zone 18 by line 20 and may be introduced into a stripping zone 21 provided with a temperature adjusting means 22 for removal of sulfur dioxide by way of line 23. The rafiinate phase substantially free from sulfur dioxide may be recovered by line 24 and will comprise substantially paraffinic and naphthenic hydrocarbons.

The extract phase is withdrawn from zone 18 by line 25 and suitably may be charged to a stripping zone 26 provided with a temperature adjusting means 27' for removal of S0 from the extract by way of line 28. The extract, substantially free of S0 is recovered by line 29 and introduced thereby into a second distillation zone 30, which is similar to distillation zone 12, and which may comprise a plurality of modern distillation towers.

Distillation zone 30 has a heating means illustrated by a steam coil 31 to allow removal as an overhead fraction a non-aromatic stream by line 32 and to allow recovery by line 33 of a fraction consisting of substantially pure benzene.

The non-aromatic stream in line 32 will comprise paraffinic and naphthenic hydrocarbons and a minor amount of benzene. This stream contains the benzene and the non-aromatic hydrocarbons in the form of azeotropes with benzene and the stream may be discarded from the system for further use or processing by opening valve 34 in line 32. Preferably the substantially non-aromatic stream is recycled to line 17 by way of branch line 35 controlled by valve 36 for re-extraction in zone 18 in admixture with the fraction in line 17. The non-aromatic stream in line 35 may, if desired, be introduced directly into zone 13.

It will be seen from the foregoing description of the drawing that a substantially pure benzene fraction is re.- covered as a bottoms fraction from a distillation zone rather than an overhead fraction from a distillation zone as is conventionally the case.

The invention will be further illustrated by an operation in which an appropriate light hydrocarbon stream is charged to a distillation column, the conditions of which are adjusted so that a fraction coming overhead has a boiling range of about 145 to about 170 F. This fraction will contain benzene and other hydrocarbons of this approximate boiling range which form azeotropes with benzene and also will contain methylcyclopentane, normal hexane, and some of the isomeric hexanes and heptanes. A preferred feed will have been depentanized prior to this distillation operation. The overhead stream boiling between about 145 and about 170 F. is then charged to a sulfur dioxide extraction zone and therein separated into a raffinate and an extract layer. The extract layer is charged to a second distillation zone for recovery of pure benzene as a bottoms fraction. Because of the solubility relationships existing in the extraction zones, the extract layer charged to the second distillation zone may contain from about 50% to about 60% by volume of benzene and from about 50% to about 40% by volume of non-aromatics. The non-aromatics distill overhead largely in the form of azeotropes with benzene. The bottoms fraction from the second distillation zone constitutes a high purity benzene.

- As a further illustration of the operation of the present invention, a virgin naphtha had pure benzene added to it to provide a fraction similar to the extract phase in line 29 of the drawing. This material contained 48% by volume of benzene and was charged to a continuous distillation operation in a 50-plate Oldershaw column operating with a 9:1 reflux ratio at a suitable temperature and pressure. A bottoms product of 98.5% benzene was obtained representing a recovery of approximately 85% of the benzene charge to the distillation column. Redistillation of the recovered benzene product to a 90% bottoms gave a product of 99% by volume of benzene.

It will be seen from the foregoing description that substantially pure benzene may be obtained without resorting to the usual complicated procedures to obtain pure benzene from petroleum hydrocarbons. Ordinarily, in extraction of hydrocarbons with sulfur dioxide to recover benzene therefrom, the maximum purity of benzene obtainable is of the order of 50% to 60%. Further purification of a benzene-sulfur dioxide extract is ordinarily achieved using the so-called wash oil technique in which a non-aromatic hydrocarbon of different boiling range is admixed with the sulfur dioxide extract to displace the non-aromatics of similar boiling range to the benzenes with non-aromatics of different boiling range which are then easily separable by distillation. The prior art procedure is objectionable, however, since it requires large volumes of wash oil because of the high concentration of non-aromatic hydrocarbons in the extract layer. It may be seen that the present invention diifers from the conventional procedures and allows the obtaining of high purity benzene by a sequence of operations in which a selected fraction is extracted with sulfur dioxide and the extract layer distilled to recover a bottoms fraction of substantially pure benzene. This is an unexpected result and is quite desirable in that unnecessary processing operations are eliminated and high purity benzene is obtained in a particular sequence of operating steps.

The nature and objects of the present invention having been completely described and illustrated, what we wish to claim as new and useful and to secure by Letters Patent is:

1. A method for recovering benzene which consists of fractionating a feed material consisting of a mixture of benzene, paraflinic and naphthenic hydrocarbons and containing a fraction of benzene and parafiinic and naphthenic hydrocarbons having six and seven carbon atoms in the molecule and boiling in the range between about 145 9 and about 170 F. extracting said fraction with liquefied sulfur dioxide in an extraction zone under conditions to form an extract phase and a raflinate phase, said extract phase containing from about 50% to about 60% by volume of benzene and from about 50% to about 40% by volume of parafiinic and naphthenic hydrocarbons, and then distilling said extract phase to recover an overhead fraction in the form of an azeotropic mixture of said paraffinic and naphthenic hydrocarbons and a minor amount of said benzene and a bottoms fraction of substantially pure benzene.

2. A method in accordance with claim 1 in which the amount of benzene in the overhead fraction is appro mately 10% by volume of the overhead fraction.

3. A method in accordance with claim 1 in which the distillation conditions include a reflux ratio in the range from about 5:1 to about 15:1.

4. A method in accordance with claim 1 in which the overhead fraction is recycled to the extraction zone.

5. A method in accordance with claim 1 in which sulfur dioxide is removed from said extract phase prior to distilling same.

6. A method for recovering benzene which consists of fractionating a feed material consisting of a mixture of benzene, parafiinic and naphthenic hydrocarbons and obtaining a mixture consisting of benzene and parafiinic and naphthenic hydrocarbons boiling in the range between about and F. extracting said mixture with liquefied sulfur dioxide in an extraction zone under conditions to form a raflinate phase and an extract phase, removing sulfur dioxide from said extract phase, said sulfur-dioxrde-free extract phase containing from about 50% to about 60% by volume of benzene and from about 50% to about 40% by volume of non-aromatic hydrocarbons, and then distilling the extract phase from which sulfur dioxide has been removed under conditions to recover an overhead fraction containing azeotropes of said benzene with said non-aromatic hydrocarbons, and a bottoms fraction of substantially pure benzene.

7. A method in accordance with claim 6 in which the overhead fraction is recycled to the extraction zone.

8. A method for recovering benzene which consists of fractionally distilling a mixture consisting of benzene, parafiinic and naphthenic hydrocarbons to recover a fraction consisting of benzene and non-aromatic hydrocarbons boiling in the range between about 145 and about 170 F., charging said fraction to a solvent extraction zone and there extracting it with liquefied sulfur dioxide under conditions to form an extract phase and a raffinate phase, removing sulfur dioxide at least from said extract phase, said sulfur-dioxide-free extract phase containing from about 50% to about 60% by volume of benzene and from about 50% to about 40% by volume of non-aromatic hydrocarbons, then distilling said extract phase from which sulfur dioxide has been removed under conditions including a reflux ratio in the range from about 5 :1 to about 15:1 to recover an overhead fraction containing azeotropes of said benzene and said nonaromatic hydrocarbons and a bottoms fraction of substantially pure benzene, and recycling the overhead fraction to said solvent extraction zone in admixture with said benzene-containing fraction.

9. A method in accordance with claim 8 in which the admixture contains about 48% by volume of benzene.

References Cited in the file of this patent UNITED STATES PATENTS 1,871,694 Ihrig Aug. 16, 1932 2,407,820 Durrum Sept. 17, 1946 2,711,433 Poifenberger June 21, 1955 2,730,558 Gerhold Jan. 10, 1956 

1. A METHOD FOR RECOVERING BENZENE WHICH CONSISTING OF FRACTIONING A FEED MATERIAL CONSISTING OF A MIXTURE OF BENZENE, PARAFFINIC AND NAPHTHENIC HYDROCARBONS AND CONTAINING, A FRACTION OF BENZENE AND PARAFFINIC AND NAPHTHENIC HYDROCARBONS HAVING SIX AND SEVEN CARBON ATOMS IN THE MOLECULE AND BOILING IN THE RANGE BETWEEN ABOUT 145* AND ABOUT 170* F. EXTRACTING SAID FRACTION WITH LIQUEFIED SULFUR DIOXIDE IN AN EXTRACTION ZONE UNDER CONDITIONS TO FORM AN EXTRACT PHASE AND A RAFFINATE PHASE, SAID EXTRACT PHASE CONTAINING FROM ABOUT 50% TO ABOUT 60% BY VOLUME OF BENZENE AND FROM ABOUT 50% TO ABOUT 40% BY VOLUME OF PARAFFINIC AND NAPHTHENIC HYDROCARBONS, AND THEN DISTILLING SAID EXTRACT PHASE TO RECOVER AN OVERHEAD FRACTION IN THE FORM OF AN AZEOTROPIC 